Winglet & Tip stall

[Mr.Vortex]

Hi all

I'm wonder that if the same airplane that equip with winglet like Boeing 737NG
tend to have tip stall characteristic more than the airplane with out winglet.
Since the effective AOA at tip is not reduce as much as the airplane without winglet. Is that right? And if it is right how they solved it.

Thanks for all reply.:O

[Pugilistic Animus]

to certify the plane they usually need an inboard section to stall first so twist is used allowing the outboard section to always remain above the aoa of the inboard section

winglets reduce induced drag coefficient by modifying the wing area without increasing the span [much]---this increase in aspect ratio reduces the effect of the vortices formed by the pressure differential between the upper and lower surface for a given alpha...the induced drag effects being worse at higher aoa---what effects such a modification has on the overall stall characteristic is really known only to the manufacturer so the final answer is I don't really know:)

[bearfoil]

Except to say that the "winglet" per se, is an add that reduces drag produced by the vortex, per PA. It produces substantial savings in SFC at cruise. The improvement is on the order of 1-3 per cent, or 2 gallons per hundred burnt. Insignificant? Not as we see it.
bear, who knows even less than PA, who knows more than he lets on.

[BOAC]

My 2 cents:

Winglets reduce the tip vortex thus reducing the effective tip AOA

and

by slowing the spanwise upper surface boundary layer flow they further delay tip stall.

Fire away, lads.

[Pugilistic Animus]

Winglets reduce the tip vortex thus reducing the effective tip AOA
just to add a little on the mechanism for this--by reduction or vortex strength you reduce the induced drag

because the span wise flow once it reaches the end of the wing meets up and twist around produces a drag force due to the acceleration created by the change in the direction of air circulation around the wing---a change in velocity vector =acceleration
this can be imagined kind of like a rope attached to the wing tips... this drag is the result of producing lift in steady state and since fundamentally less drag produced results a lower induced angle of attack---and a lower alpha effect as BOAC and Bearfoil have mentioned

however the overall effects of winglets on stall qualities is probably relatively insignificant due to being overridden by the much more influential effects of twist [to meet stability requirements] as to not make much of a difference...also with just one winglet most aircraft only exhibit a minor handling difference wrt to trim..so they don't seem to cause very large aerodynamic changes---my guess

note winglets are mainly used to control aspect ratio a major player in the induced drag coefficient[ Cdi ]since most airplanes don't exhibit a rectangular planform---- Aspect Ratio [AR or A] is defined for a non-rectangular wing as the ratio of span squared/wing area or b^2/S
so, although span is not increased by much the wing area 'S' is increased thereby lowering the induced drag coefficient and consequently the induced aoa-:8:O


:)